Slides on various network access technologies.
DSL (Digital Subscriber Line) subsumes all layer 1 and 2 technologies for transporting digital data over (twisted pair) copper wires. In traditional telephone networks, pairs of copper wire run from a central location (Central Office) to subscriber premises. Although initially designed for 300Hz to 3.4kHz bandwidth, these copper wires could be upgraded to Internet access lines through the use of DSL technologies. While early DSL technologies like HDSL required 4 copper wires, newer technologies like ADSL (Asymmetric Digital Subscriber Line), SDSL (Symmetric Digital Subscriber Line) and VDSL (Very High Datarate Digital Subscriber Line) only require a single local loop line (pair of copper wires). Technological advances in digital signal processing and CPU speed increased possible data rates dramatically. ADSL2+ (ITU-T G.992.5) allows downstream data rates up to 24MBit/s on short distances (1-2km).
Read More Download PDFDSL (Digital Subscriber Line) subsumes all layer 1 and 2 technologies for transporting digital data over (twisted pair) copper wires. In traditional telephone networks, pairs of copper wire run from a central location (Central Office) to subscriber premises. Although initially designed for 300Hz to 3.4kHz bandwidth, these copper wires could be upgraded to Internet access lines through the use of DSL technologies. While early DSL technologies like HDSL required 4 copper wires, newer technologies like ADSL (Asymmetric Digital Subscriber Line), SDSL (Symmetric Digital Subscriber Line) and VDSL (Very High Datarate Digital Subscriber Line) only require a single local loop line (pair of copper wires). Technological advances in digital signal processing and CPU speed increased possible data rates dramatically. ADSL2+ (ITU-T G.992.5) allows downstream data rates up to 24MBit/s on short distances (1-2km).
Read More Download PDFSerial and dial-up lines do not provide a framing. Instead they offer only a raw bit transport service. Therefore a framing protocol is needed so that the receiver can detect frame (packet) boundaries. SLIP (Serial Line IP) was an early and very simplistic protocol that provided this framing. PPP (Point to Point Protocol) is a successor to SLIP. PPP is a collection of protocols each providing a specific function like authentication, link layer negotiation or compression.
Read More Download PDFThe term AAA (say triple A) subsumes the functions used in network access to allow a user or a computer to access a network and use its resources. AAA stands for Authentication (is the user authentic?), Authorization (what is the user allowed to do?) and Accounting (track resource usage by the user). AAA is typically employed at network ingress points to control user's access to the network and resources. The most prominent protocol for AAA is RADIUS (Remote Authentication Dial In User Service) which defines messages for opening and closing a network session and counting network usage (packet and byte count). RADIUS usually works in conjunction with an LDAP server that stores the policies and user authorizations in a central repository.
Read More Download PDFDynamic IP address assignment to a host (or interface) is a common problem in TCP/IP based networks. Manual and static assignment of IP addresses does not scale well and becomes a labor intensive task with a growing number of hosts. An early approach for dynamic IP address assignment was RARP (Reverse ARP) which ran directly on the Ethernet protocol layer. The many problems of RARP such as the inability to be routed between subnets were solved with BOOTP (Bootstrap Protocol). BOOTP, however, ended to have its own set of limitations like lack of a lease time for IP addresses. DHCP (Dynamic Host Configuration Protocol) was therefore defined as an extension to BOOTP. DHCP is backward compatible with BOOTP thus allowing some degree of interoperability between the 2 protocols. The state-of-the-art protocol for dynamic IP address assignment is, however, is DHCP. DHCPv6 is an adaption of DHCP for IPv6 based networks.
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