WAN Technologies

Features of WAN

WAN is a network that spread over large geographical area. It uses several technologies to get that connectivity over vast area. From that connectivity we can have lot features in WAN. They are,

Circuit switching

Packet switching

Lease line

X.25

Frame relay

ATM

Circuit switching

Circuit switching involves creating a direct physical connection between sender and receiver. The connection must be set up before any communication can occur. A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. 

Circuit switching

The sender and receiver can count on "owning" the bandwidth allotted to them for as long as they remain connected.

Packet switching

Packet switching is a WAN technology in which users share common carrier resources. Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Packet Switching allows the same data path to be shared among many users in the network.

 

Packet Switching

 

The packet passes from exchange to exchange for delivery through the provider network. This data packets change the path dynamically. According to the traffic it changes the path.

Lease line

Lease line is used to provide point-to-point dedicated network connectivity. Analog leased line can provide maximum bandwidth of 9.6 Kbps. Digital leased lines can provide bandwidths: 64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3) ... Internet lease line is used to access internet with dedicate bandwidth.

X.25

X.25 Defines a telephone network for data communications. It provides users with WAN connectivity across public data networks (TELENET, TYMNET). Developed by common carriers to increase subscription to PDNs. Specification defines a point-to-point interaction between DTEs and DCEs for remote access terminals and computers.

Thank you all

Comments are welcome

Internet access Technologies in Sri Lanka

 

Internet access Technologies in Sri Lanka

Broadband Technologies

ADSL - Uses typical twisted pair cable that come home. Maximum downstream up to 8 Mbps. Divide the voice and data signals on the telephone line into three frequency bands.

Internet Leased Line - Internet leased lines are usually available at speeds of 64k, 128k, 256k, and 512k, T1 or E1).

Optical Fiber - Technology which bring fiber step closer to the subscriber. In Sri Lanka vastly use in large organizations. Can go up to speed of up to 1 Gbps

HSPA - Supports data rates up to 27 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. In Sri Lanka do not provide unlimited packagers.

Wi-Max - Can go for over a much greater range.  Point-to-multi point: last-mile internet access.  People can go up to 52 Mbps. Good solution for the people who can’t get ADSL connection due to long distance.

LMDS - LMDS offers a microwave solution with a reduced cost per link. It transmits in a point to multi-point fashion over a wide coverage area.  LMDS channel is capable of 45 Mbps downstream.

CDMA - Can achieve maximum capacity of 2Mbps. Popular as wireless internet access technology in Sri Lanka.

Wi-Fi - Based on the IEEE 802.11x standard and transmitting in unlicensed spectrum at 2.4 GHz. support data rates up to 54 Mbps.

Narrow Technologies

Dial-up - Uses the facilities of the public switched telephone network (PSTN). Use same frequency voice band of 0- 4 kHz. Few years ago very popular, but only can have 56 kbps.

ISDN - Much faster speed of 256 kbits/s. But not considered as broadband. Not popular because had to use separate equipments.

WAP - Most use of WAP involves accessing the mobile web from a mobile phone. People can’t go much capacity through this wireless mobile technology.

GPRS - Can achieve maximum speeds of up to 9.6 kbps. This is mobile wireless technology.  Mainly used   for web browsing.

xDSL Family

ADSL - Asymmetric Digital Subscriber Line

RADSL - Rate adaptive Digital Subscriber Line

VDSL - Very high Bit rate Digital Subscriber Line

HDSL - High Bit rate Digital Subscriber Line

SDSL – Symmetric Digital Subscriber Line

There are some characteristics included in all of the DSL technologies. When we consider the bandwidths of these DSL technologies are depends on the length of the loop (distance to the central office from the user end). 

ADSL

In ADSL there are many versions. They are ADSL, ADSL2, ADSL2+, The Downlink and Uplink will depend on this versions. The data transfer rates downstream are much faster than the upstream data rates in ADSL.

The data rate of ADSL is highly dependent upon the distance from the Central Office (CO) to the Consumer Premises (CPE). At a distance of 9000 ft we can achieve 8 Mbps downstream and while at 18000 ft we can only get 1.544 Mbps downstream. ADSL operates at frequencies above 4 kHz, typically from 30 kHz to 1.1 MHz (Upstream is in the range from 30 kHz to 138 kHz, downstream ranges from 138 kHz, to ~1.1 MHz).

Applications

ADSL is used by home consumers and many small business owners who mainly want to download files. It is used for carrying voice, data and video at reasonable rate. We can download large data files, streaming video, audio, and multimedia from the Internet fast. But, generally, cannot upload much more than e-mail messages.

 RADSL

RADSL stands for Rate Adaptive Digital Subscriber Line. Rate Adaptive simply means that the speed of the connection is adjusted to meet the line conditions that each transmit and receive unit sees. And the upstream is 128kbps – 1Mbps and downstream 600kbps – 7Mbps.RADSL same as ADSL but the distance will increase due to adjustment of streams.

Applications

RADSL is used by home consumers and many small business owners who mainly want to download files and small uploads. It is used for carrying voice, data and video at reasonable rate.

VDSL

This is the fastest DSL technology. VDSL stand for Very high bit-rate Digital Subscriber Line. Not like other DSL technologies the capacity of the link depends on the service offering and spectrum regulations. It has 55.2 Mbps of download speed and 16 Mbps Upstream over single twisted pair. And it has 34 Mbps of download speed and upstream if the link is symmetric. It uses much wider bandwidth than ADSL IT also depends on loop condition.

Applications

VDSL is capable of supporting high bandwidth applications such as HDTV as well as telephone services (VOIP) and high quality video conferencing.

HDSL

HDSL stands for High-bit-rate Digital Subscriber Line. The main characteristic of HDSL is that it is symmetrical. That means an equal amount of bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.

The primary disadvantage of HDSL is that it requires two twisted pairs of wires to operate, which increases the deployment cost for service providers. Also, HDSL does not support Plain Old Telephone Service (POTS) on the same lines as the data.

Applications

It uses for business applications, server access in large organizations and traditional T1 roles.

SDSL

SDSL Broadband provides a high-speed internet access service, with matching upstream and downstream data rates ranging from several speeds from 128kbit/s to 2Mbit/s. Unlike ADSL, it cannot co-exist with a conventional voice service on the same pair as it takes over the entire bandwidth. So using your phone line and the SDSL simultaneously is impossible. It typically falls in price between ADSL and T-1, and it is mainly targeted at small and medium businesses who may host a server on site.

Applications

Medium businesses who need to host a server on site, high quality video conferencing and multiple voice lines.

Access Network

 Access Network

We learn about basic network in basic telecommunication networks to understand their principals and operation. The main and the very important network is access network when someone on the basic learning.

An access network (Outside Plant) is the network that has series of wires, cables and equipment lying between a consumer and service operator. This is the only one network customer can see from this eyes. 

Block Diagram of Access Network

Exchange – Exchange is he center where the switching equipments and DSLAM placed. Switching equipment connects the customer to caller party by analyzing the dialed number. And DSLAM is used to provide the DSL service to customers. And MDF stands for main distribution frame. The MDF is a termination point within the local telephone exchange where exchange equipment and terminations of local loops are connected by jumper wires at the MDF. 

Street cabinet - Street cabinet is the device located in the street in between local exchange and the customer. Big size cables having much number of pairs are terminated at cabinets and they are distributed to different customer’s locations through smaller size cable having lesser number of cable pairs.

DP – DP stands for Distribution point. DP is used for termination of secondary telephone network to the subscriber drop or service line cable pairs.

Drop wire – Drop wire ends the access network. It is used to connect customer premises equipment with Distribution point.

Customer premises equipment (CPE) - customer premises equipment are Discharger, Rosette box, Splitter, and modem. 

Access Network

 

Today service operators supply additional services such as xDSL based broadband and IPTV (Internet Protocol Television) to customers using access network. The access network is again the main barrier to achieving high data rate to customers, because even though providers configure and update their core network there can be lot of issues in access network due to structure of the cabling and high attenuation. Without understanding or even knowing the characteristics of these enormous copper spider webs, it is very difficult, and expensive to connect new customers and assure the data rates required to receive next generation services.

Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

Teletraffic Engineering

Today I’m going to explain some important words and their definitions in Tele-traffic engineering. These terms are very important and extremely useful when calculating offered traffic in a trunk or getting calculations.

Congestion

Congestion occurs when the number of packets being transmitted through the network approaches the packet handling capacity of the network. Most networks starts dropping packets when they are overloaded and this phenomenon is called congestion.

Networks provide congestion –control mechanism to prevent this problem. Congestion control aims to keep number of packets below a level at which performance falls off dramatically.

The congestion in the packet switching network appears due to packet handling capacity of the network while transmission of the packets. When too many packets are present in the subnet the performance get reduced. Most networks start dropping packets when they are overloaded. It happens when packet arrival rate exceeds the outgoing link capacity. This is this is called congestion in handling of packets.

  

Choke packets

Choke packets refer to the packets sent to a transmitter to tell it that congestion exists and that should reduce its sending rate. This is a specialized packet that is used for flow control along a network. A router detects congestion by measuring the percentage of buffers in use, line utilization and average queue lengths. When it detects congestion, it sends choke packets across the network to all the data sources associated with the congestion. The sources respond by reducing the amount of data they are sending.

           But this is not strong enough to long distance and high speeds, the choke packets are not very effective and also these packets are a more direct way of telling the source to slow down. This controlling packet is generated at a congested node and transmitted to restrict traffic flow.

Random early discard

        Random early discard (RED), also known as random early detection or random early drop is an active queue management algorithm. It is also a congestion avoidance algorithm.

In the traditional tail drop algorithm, a router or other network component buffers as many packets as it can, and simply drops the ones it cannot buffer. If buffers are constantly full, the network is congested. Tail drop distributes buffer space unfairly among traffic flows. Tail drop can also lead to TCP global synchronization as all TCP connections "hold back" simultaneously, and then step forward simultaneously. Networks become under-utilized and flooded by turns. RED addresses these issues.

                       

Traffic Shaping

                            Traffic shaping is an attempt to control network traffic in order to optimize or guarantee performance, low-latency, and/or bandwidth. Traffic shaping deals with concepts of classification, queue disciplines, enforcing policies, congestion management, quality of service (QoS), and fairness.

                                  Traffic shaping is any action on a set of packets (often called a stream or a flow) which imposes additional delay on those packets such that they conform to some predetermined constraint (a contract or traffic profile).Traffic shaping provides a means to control the volume of traffic being sent into a network in a specified period (bandwidth throttling), or the maximum rate at which the traffic is sent (rate limiting).

       

Difference between two traffic shaping algorithms

                     

Leaky bucket and Token buket

Token bucket throws away tokens when the bucket is full but never discards packets while leaky bucket discards packets when the bucket is full. Unlike leaky bucket, token bucket allows saving, up to maximum size of bucket n. This means that bursts of up to n packets can be sent at once, giving faster response to sudden bursts of input. Leaky bucket forces bursty traffic to smooth out, token bucket permits burstiness but bounds it. Token bucket has no discard or priority policy.

          Token bucket when compared to leaky bucket, is easy to implement. Each flow needs just a counter to count tokens and a timer to determine when to add new tokens to the counter.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.