vault backup: 2025-12-31 15:35:50

Author: adielbm

notes/.obsidian/community-plugins.json

@@ -8,5 +8,6 @@
   "sheets",
   "img-caption",
   "dark-mode-images",
-  "execute-python"
+  "execute-python",
+  "bibliography"
 ]

notes/Computer Networks/Link layer.md

@@ -5,14 +5,13 @@
 	- Backbone
 	- LAN
 
-
 ## Framing 
 
 - A **frame** 
 
 #### Point-to-Point Protocol (PPP)
 
-Byte-Oriented
+- PPP is a byte-oriented protocol
 
 <table>
   <tr>
@@ -44,25 +43,43 @@ Byte-Oriented
 
 
 - Link Control Protocol (LCP)
+	- "A PPP protocol responsible for establishing, maintaining, configuring, and terminating links" [@Forouzan, 2012]
 
 #### High-Level Data Link Control (HDLC)
 
-bit-oriented
+- **High-Level Data Link Control** (**HDLC**)
+- HDLC is a bit-oriented protocol
 
 ## Error detection and correction
 
 
-
-- A **message** (סיביות מידע, מילת מידע) $M$ of length $m$.
-- **Redundant bits** (סיביות ביקורת) $R=f(M)$ of length $r$ (where $r \ll m$). 
-- The sender transmits the **codeword** (מילת קוד) $P = (M,R)$ of length $n=m+r$. 
-- The receiver receives $(M',R')$ and checks if $R' = f(M')$, if yes, assume no error with high probability, else, error detected.
+- **error detection and correction** (**EDAC**) (or **error control**)
+	- "The handling of errors in data transmission." [@Forouzan, 2012]
+- Error-detection codes
+- **forward error correction** (FEC)
+	- "The process that enables a receiver, upon detecting an error in the arriving data, to correct the error without further information from the transmitter." [@West, 2021] 
+	- "Correction of errors at the receiver without retransmission." [@Forouzan, 2012]
+- **error-correction codes** (or **error-correcting codes**) (ECC)
+
+- **data bits** (or **dataword** or **message** or **(data) block**) (סיביות מידע, מילת מידע) 
+	- $M$ of length $m$.
+- **redundant bits** (or **redundancy**) (סיביות ביקורת) 
+	- $R=f(M)$ of length $r$ (where $r \ll m$). 
+- sender: 
+	- transmits the **codeword** (מילת קוד) $P = (M,R)$ of length $n=m+r$. 
+- receiver: 
+	- receives $(M',R')$
+	- checks if $R' = f(M')$, 
+		- if yes, assume no error with high probability, 
+		- else, error detected.
+- There can be $2^m$ possible datawords, and $2^n$ possible codewords.
+	- Thus, there are $2^{n}-2^{m}$ **invalid** codewords that can be used to detect errors.
 - (**code rate**) $R_{c}=\frac{m}{n}$
 - (**overhead**, תקורה) $\frac{r}{n}$
-- (**redundancy**) $\frac{r}{m}$ 
+- (**redundancy**, יתירות) $\frac{r}{m}$ 
 
 - A **bit error** is when a bit is received incorrectly (0 instead of 1 or vice versa)
-- A **burst error** is when a sequence of bits is received incorrectly
+- A **burst error** (or **error burst**) is when a sequence of bits is received incorrectly
 - (**bit error ratio**) $\displaystyle\text{BER} = \frac{\text{\# bit errors}}{\text{Total transmitted bits}}$
 - (**bit error probability**) $p_{e}=\mathrm{E}[\text{BER}]$
 
@@ -77,7 +94,7 @@ bit-oriented
 	- $\displaystyle s = d_{\min} - 1$ 
 - The **minimum Hamming distance** of a code $\mathcal{C}$ is $\displaystyle d_{\min} = \min_{c_1 \neq c_2 \in \mathcal{C}} d(c_1,c_2)$.
 
-נצילות השידור
+
 ### parity checks 
 
 
@@ -118,11 +135,12 @@ bit-oriented
 
 
 
-
-
 ## Error control 
 ### Stop-and-wait ARQ
 
+- **stop-and-wait**
+	- "A protocol in which the sender sends one frame, stops until it receives confirmation from the receiver, and then sends the next frame" [@Forouzan, 2012]
+
 
 ```
 sender:
@@ -174,8 +192,8 @@ receiver:
 	- invariant:
 		- $\textsf{LAF} - \textsf{LFR} \leq \textsf{RWS}$
 
-
-- $\textsf{SWS} < \frac{1}{2} \times (\text{MaxSeqNum}+1)$ 
+- to fully utilize the link the SWS must be at least the bandwidth-delay product (in frames) 
+- $2\times \textsf{SWS} < (\text{MaxSeqNum}+1)$ 
 
 
 - negative acknowledgment

notes/Computer Networks/Performance.md

@@ -14,7 +14,7 @@
 $$\text{Latency} = t_{\text{prop}} + t_{\text{tx}} + t_\text{queue}$$
 - **latency**
 	- the amount of time it takes for a packet of data to travel between two points across a network connection
-	- "_The delay between the transmission of a signal and its receipt_" [^1]
+	- "_The delay between the transmission of a signal and its receipt_" [@West, 2021]
 	- 
 - latency (also called delay (?) #todo) is the time it takes for data to pass from one point on a network to another
 - (**Propagation delay**) $t_{\text{prop}} = \frac{d}{v}$
@@ -43,7 +43,11 @@ $$\text{Latency} = t_{\text{prop}} + t_{\text{tx}} + t_\text{queue}$$
 
 #### Bandwidth-delay product
 
-- The **bandwidth-delay product**, $\text{RTT}  \times \text{bandwidth}$, in bits, is the amount of data that can be in transit in the network at any given time
+- **bandwidth-delay product** (in bits)
+	- $\text{RTT}\times\text{bandwidth}$
+	- the amount of data that can be in transit in the network at any given time
+	- "The bandwidth-delay product defines the number of bits that can fill the link." [@Forouzan, 2012]
+	- link utilization = $\displaystyle\frac{\text{data in flight}}{\text{bandwidth-delay product}}$
 
 
 
@@ -72,4 +76,3 @@ $$\text{Latency} = t_{\text{prop}} + t_{\text{tx}} + t_\text{queue}$$
 
 - (**Channel utilization**) $U=\frac{\text{throughput}}{R}$
 
-[^1]: West, J. (2021). _Data communication and computer networks: A Business User’s Approach_. Course Technology.

notes/Computer Networks/intro.md

@@ -56,9 +56,9 @@
 
 
 - **protocol data unit (PDU)**
-	- _"The combination of data from the next higher layer and control information"_ [^1]
-	- _"Another name for a packet or frame"_. [^2] 
-	- _"A PDU at layer $N$ is a message sent between protocols at layer $N$. It consists of layer $N$ header information and an encapsulated message from layer $N+1$, which is called both the layer $N$ SDU and the layer $N+1$ PDU"_. [^3]
+	- _"The combination of data from the next higher layer and control information"_ [@Stallings, 2013]
+	- _"Another name for a packet or frame"_. [@Peterson, 2020]
+	- _"A PDU at layer $N$ is a message sent between protocols at layer $N$. It consists of layer $N$ header information and an encapsulated message from layer $N+1$, which is called both the layer $N$ SDU and the layer $N+1$ PDU"_. [@Kozierok, 2005]
 - **service data unit (SDU)**
 - (**packet**) 
 	- (1) _a generic term used to describe unit of data at all levels of the protocol stack_. ([RFC 1594](https://www.rfc-editor.org/rfc/rfc1594.html))
@@ -67,6 +67,8 @@
 	- a synonym with _packet_
 	- connectionless communication, packet-switched network
 	- _"A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network"_. ([RFC 1594](https://www.rfc-editor.org/rfc/rfc1594.html))
+- (**frame**) 
+	- "A packet at the data-link layer is normally called a _frame_." [@Forouzan, 2012]
 
 
 - **Best-effort service**
@@ -83,13 +85,19 @@
 	- **Connectionless-mode Network Service** (**CLNS**) (or simply **Connectionless Network Service**)
 
 
+- **bit stuffing**
+	- "A technique used to distinguish control sequences and data on the bit level." [@Peterson, 2020]
+	- "In a bit-oriented protocol, the process of adding an extra bit in the data section of a frame to prevent a sequence of bits from looking like a flag." [@Forouzan, 2012]
+- **byte stuffing**
+	- "The process of adding one extra byte whenever there is a flag or escape character in the text." [@Forouzan, 2012]
+	- "In a byte-oriented protocol, the process of adding an extra byte in the data section of a frame to prevent a byte from looking like a flag." [@Forouzan, 2012]
+- **bit-oriented protocol**
+	- "A protocol in which the data frame is interpreted as a sequence of bits" [@Forouzan, 2012]
+- **byte-oriented protocol**
+	- "A protocol in which the data section of the frame is interpreted as a sequence of bytes (characters)." [@Forouzan, 2012]
+
 
-[[Transport layer]]
-# Internet layer
 
 
-[^1]: Stallings, W. (2013). _Data and computer communications_.
 
-[^2]: Peterson, L. L., & Davie, B. (2020). _Computer networks: A Systems Approach_. Morgan Kaufmann Publishers.
 
-[^3]: Kozierok, C. M. (2005). _The TCP/IP guide: A Comprehensive, Illustrated Internet Protocols Reference_. No Starch Press.