Intenet Access Technologies in Srilanka

Internet access Technologies	Broadband	Narrow-band	Description
ADSL	Yes		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	Yes		Internet leased lines are usually available at speeds of 64k, 128k, 256k, and 512k, T1 or E1). Any speed required. Permanently connected to the other
Optical Fiber	Yes		Technology which bring fiber step closer to the subscriber. In Sri Lanka vastly used in large organizations. Can go up to speed of up to 1 Gbps
HSPA	Yes		Supports data rates up to 14 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. In Sri Lanka do not provide unlimited packagers.
Wi-Max	Yes		Can go for over a much greater range.  Point-to-multipoint last-mile internet access. Can go up to 11.3 Mbps. Good solution of people who cant get ADSL
LMDS	Yes		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	Yes		Can achieve maximum capacity of 2Mbps. Popular as wireless internet access technology in Sri Lanka.
Wi-Fi	Yes		Based on the IEEE 802.11x standard and transmitting in unlicensed spectrum at 2.4 GHz. support data rates up to 54 Mbps.
Dial-up		Yes	Uses the facilities of the public switched telephone network (PSTN). Use same frequency voice band of 0- 4 kHz. Few years ago very popular and only can have 56 kbps.
ISDN		Yes	Much faster speed of 256 kbits/s. But not considered as broadband. Not popular because had to use separate equipments.
WAP		Yes	Most use of WAP involves accessing the mobile web from a mobile phone. Can’t get much capacity through this wireless mobile technology.
GPRS		Yes	Can achieve maximum speeds of up to 9.6 kbps. This is mobile wireless technology.  Mainly used   for web browsing.

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.

Time Switching & Space Switching

Space switching

When we consider Space switching there is a dedicated path (two parallel wires) established between the caller and called subscribers for the entire duration of call in the exchange by the switch. It was originally designed for analog networks, but is used currently in both digital and analog switching. This means then the conversation is going on the switch create the link between two sides. At that time only that call is going in the path.

Space switching

 

Time switching

When we consider Time switching, it was coming when the PCM is introduced. This switching system involves the sharing of cross points for shorter periods of time. It uses to interchange time slots. When the E1 are coming to the Switch, it routs the path accordion to the number. In this switching all the components are electronics. Therefore, in time division switching, greater savings in cross points can be achieved. Hence, by using dynamic control mechanisms, a switching element can be assigned to many inlet-outlet pairs for few microseconds.

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.