Layer 2 > Point To Point
Frame Check Sequence (FCS)
A 16 or 32 bit checksum computed over the frame to provide basic protection against errors in transmission. This is a CRC code similar to the one used for other layer two protocol error protection schemes such as the one used in Ethernet.
Link Control Protocol (LCP) is used by PPP to negotiate and setup control options on the WAN data link. It sits on top of the physical layer and is used to establish, configure, and test the data-link connection.
Network Control Protocol (NCP) is used by PPP to encapsulate and negotiate options for multiple network layer protocols , for every network layer protocol used, a separate NCP is provided.
Password Authentication Protocol (PAP) is a simple authentication protocol used to authenticate a user using a 2 way handshake and no encryption.
Challenge-Handshake Authentication Protocol (CHAP) is a secure authentication protocol using a 3 way handshake , with a challenge , shared secret and encryption.
Signaling methods :
Nonreturn to Zero Level NRZ-L
High Density Binary 3 HDB3 (E1)
Binary 8 With Zero Substitution B8ZS (T1)
Alternative Mark Inversion AMI
Compression :
Stacker
Predictor
Committed Information Rate (CIR) is a guaranteed connection
rate and Extended Information Rate (EIR) is an allowance of
burstable bandwidth.
The provider guarantees that the connection will always support the CIR rate,
and sometimes the EIR rate should there be adequate bandwidth.
Frames that are sent in excess of the CIR are marked as "discard eligible"
(DE) which means they can be dropped should congestion occur within the frame
relay network. Frames sent in excess of the EIR are dropped immediately.
Local Management Interface (LMI) is a signaling standard used between
routers and frame relay switches. Communication takes place between a router
and the first frame relay switch it's connected to. Information about keepalives,
global addressing, multicasting and the status of virtual circuits is commonly
exchanged using LMI.
3 standards
- ANSI's Annex D standard,
- T1.617, ITU-T's Q.933 Annex A standard,
- the "Gang of Four" (Cisco, DEC, StrataCom and NorTel)
HDLC / LAPB / PPP
I-Frames
(Information frames):
Carries upper-layer information and some control information , functions include
sequencing, flow control, and error detection and recovery. I-frames carry send
and receive sequence numbers.
S-Frames (Supervisory Frames): Carries control information, functions
include requesting and suspending transmissions, reporting on status, and acknowledging
the receipt of I-frames. S-frames carry only receive sequence numbers.
U-Frames (Unnumbered Frames): carries control information ,
functions
include link setup and disconnection, as well as error reporting. U-frames carry
no sequence numbers
PSTN (ISDN) / (PPP)
Time-division
multiplexing (TDM) is
the transmission of several sources of information using one common channel,
or signal, and then the reconstruction of the original streams at the remote
end. Depending on whether bits or bytes are used, TDM is called bit-interleaving
or byte-interleaving.
Statistical Time-division Multiplexing (STDM) is an advanced
version of TDM in which both the address of the terminal and the data itself
are transmitted together for better routing. Using STDM allows bandwidth to
be split over 1 line.
FIBER / ATM
Wavelength
Division Multiplexing (WDM) where
signals transmitted across the fibre are transmitted at different wavelengths,
creating additional channels for transmission
Plesiochronous Digital Hierarchy (PDH) was developed as a standard
for multiplexing higher order frames creating larger numbers of channels by
multiplexing the standard EU 30 channel TDM frames.
Synchronous Digital Hierarchy (SDH) Synchronic transmission
and multiplex system eplacing PDH and operating at speeds of between 155 Mbits/s
amd (so far) 2.54 Gbits/s in EU
Synchronous Optical Networking (SONET) defines a set of transmission
rates, signals and interfaces for fiber optic transmission in the US
that allow data streams at different rates to be multiplexed. It establishes
Optical Carrier (OC) levels from 51.8 Mbps to 2.48 Gbps (10 Gbps for OC-192).